Thanks very much, Gena! By jumping back and forth between what you've
written and the POV-Ray docs, I've learned a bit.

I've got my display_gamma set to 1.8, which is appropriate for my system,
which means that I've got POV's equivalent of an artist's studio with large
north-facing windows: a neutral environment for selecting colors and
brightness levels. When I use assumed_gamma 1, POV will use my display_gamma
without any further adjustment to correct the pixels it writes to the image
file. The result will be the best I can hope for in terms of viewabiltiy on
other systems. If I want to tune my jpgs to look their best on PC systems,
then I should set the assumed_gamma to 2.2 (and accept that fact that Mac
users will see a poorer image).

If I have chosen the .png format, POV will also write the appropriate gamma
correction factor into the image file. Then anybody who is using viewing
software that is smart about .png gamma corrections and correctly set up on
their system will see my image precisely the way I intended. But other than
in this situation, my work is going to be distorted on some other systems.

It seems to me that in a cooperative creation process, the people doing the
textures need to have their display_gamma settings correctly tuned for their
systems, and use assumed_gamma 1 in their output.

It also seems to me that in a cooperative situation, decisions on the
assumed_gamma level cannot be based on how jpgs look, since Macs and PCs and
other systems will always distort jpgs in different ways. The decisions need
to be made either on the basis of .png files displayed through a smart
viewer that is correctly configured for the individual system, or by sending
out .pov files that each contributor would render on their own (assuming
they have their display_gamma set correctly). Sending out sample .pov files
shouldn't be too difficult.

Does this sound right to you?



--
Will Woodhull
Thornhenge, SW Oregon, USA
willl.at.thornhenge.net

"Gena Obukhov" <obu### [at] mailcom> wrote in message
news:3E9A5D93.B10D1E84@mail.com...
> Will W wrote:
>
> > supposed to even things up. I *think* that means that assumed_gamma 1
will
> > be right for anybody who has adjusted their monitor as suggested in the
POV
> > docs-- http://www.povray.org/documentation/view/128/ -- section
5.2.2.2.2.2
>
> You are talking about  Display_gamma which works together with
> assumed_gamma. That gamma stuff was always a 'terra incognita'
> for me :)
>
> I think the main confusing definition in assuming_gamma is that
> it 'resolves the problem with brightness of images on different
> platforms'. But it's actually not true unless you use format containning
> gamma info (e.g. PNG). If you use JPG it will be normal on PC but still
> bright on Macintosh. So IMHO for viewing final image in non-gamma format
> it doesn't help.
> It helps when you render image on different platforms. In this case you
> can set assumed_gamma=1 and set different Display_Gamma on different
> platforms, for example 2.2 on PC and 1.8 on Macintosh. In this case
POV-Ray
> will create image based on your Display_Gamma settings. So actual value
> which you have to play with is Display_Gamma not assumed_gamma which
> should be usually equal 1.
>
> Please correct me if I'm wrong :)
>
> Gena.

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